Process for preparing polyethylene terephthalate of improved color

ABSTRACT

A process for preparing polyethylene terephthalate wherein dimethyl terephthalate is reacted with ethylene glycol to form an ester of ethylene glycol and dimethyl terephthalate or where terephthalic acid is reacted with ethylene glycol to form an ester of terephthalic acid and ethylene glycol where the resulting ester is polycondensed in the presence of a polycondensation catalyst, the improvement comprising carrying out the condensation or polymerization of the ester in the presence of a catalytic amount of a novel catalyst mixture comprising (1) an antimony compound and (2) an arsenic compound.

Ventura et al.

1 1 PROCESS FOR PREPARING POLYETHYLENE TEREPI-ITHALATE OF IMPROVED COLOR [75] Inventors: John J. Ventura, Eatontown; Philip H. Ravenscroft, Edison, both of NJ.

[73] Assignee: M & T Chemicals Inc., Greenwich,

Conn.

[22] Filed: June 16, 1969 [21] Appl. No.: 833,805

[52] US. Cl 260/22 CA; 260/45.75 B; 260/75 R [51] Int. Cl C08g 17/013 [58] Field of Search 260/22 C, 75

[56] References Cited UNITED STATES PATENTS 3,321,444 5/1967 Hoyer et a1. 260/75 3,346,541 10/1967 Davies et a1. 260/75 3,408,333 10/1968 Tiedtke et al..... 260/75 3,412,066 11/1968 Schnegg et a1.... 260/47 3,415,860 12/1968 Thomas 260/446 3,425,995 2/1969 Carter et al.... 260/75 3,428,587 2/1969 Piirma 260/22 3,438,944 4/1969 Stewart et a1. 260/75 3,438,945 4/1969 Stewart et a1. 260/75 3,451,971 6/1969 Lazarus 260/75 51 May 20, 1975 3,457,237 7/1969 Dobinson et al 260/75 3,509,099 4/1970 Carter et a1. 260/75 R FOREIGN PATENTS OR APPLICATIONS 1,013,573 12/1965 United Kingdom 260/75 R 847,059 9/1960 United Kingdom 260/22 1,010,175 11/1965 United Kingdom 260/22 1,035,999 7/1966 United Kingdom 260/22 Primary ExaminerRonald W. Griffin Attorney, Agent, or Firm-Robert P. Auber; Kenneth G. Wheeless; Robert Spector [57] ABSTRACT A process for preparing polyethylene terephthalate wherein dimethyl terephthalate is reacted with ethylene glycol to form an ester of ethylene glycol and dimethyl terephthalate or where terephthalic acid is reacted with ethylene glycol to form an ester of terephthalic acid and ethylene glycol where the resulting ester is polycondensed in the presence of a polycondensation catalyst, the improvement comprising carrying out the condensation or polymerization of the ester in the presence of a catalytic amount of a novel catalyst mixture comprising (1) an antimony compound and (2) an arsenic compound.

7 Claims, No Drawings PROCESS FOR PREPARING POLYETHYLENE TEREPHTHALATE OF IMPROVED COLOR This invention relates to an improved method for the preparation of' polyethylene terephthalate. More particularly, this invention relates to an improved polycondensation catalyst system for use in the manufacture of polyethylene terephthalate exhibiting highly desirable color characteristics, said novel catalytic composition comprising a mixture of (1) an antimony compound and (2) an arsenic compound.

It is known that polyethylene terephthalate can be prepared from a suitable methyl ester of terephthalic acid formed by initially reacting methyl alcohol with terephthalic acid. When a methyl ester of terephthalic acid is used as a starting material, it is first reacted with ethylene glycol in the presence of a transesterification catalyst by means of an ester interchange reaction. When terephthalic acid, itself, is used as a starting material, it is subjected to a direct esterification reaction with ethylene glycol in the presence of what is generally called the first stage catalytic additive or ether inhibitor. In either method the resulting reaction product, an ester, is then polycondensed in the presence of a polycondensation catalyst to form polyethylene terephthalate.

Heretofore various materials have been suggested as polycondensation catalysts for polycondensing the ester products of both the transesterification method and the direct esterification method of preparing esters. However, in general, none of the substances that have been suggested as polycondensation catalysts have heretofore proved entirely satisfactory. The most deleterious result of the catalysts of the prior art has been the unsatisfactory color of the resulting polymer.

It is essential that for particular uses, that polyethylene terephthalate should exhibit a high degree of luminance together with a low degree of yellowness. Luminance (Y on the OLE. System) is a measure of the proportion of the incident light reflected. Yellowness is a measure, based on C.I.E. chromaticity co-ordinates, of the separation of the point representing the color rating of the polymer from the point representing a standard illuminant C. Positive values are measured in the direction of a dominant wave length of 580590 millimicrons and negative values are measured in the direction of a dominant wave length of 470-490 millimicrons. Relatively small variations in the luminance and yellowness values of polyethylene terephthalate are of great importance in deciding the value of such polyesters for commercial purposes. A useful criterion for the color of polyethylene terephthalate is obtained by subtracting the yellowness value from the luminance value. The best color for polyethylene terephthalate is obtained when the luminance value minus the yellowness value is at a maximum.

It is an object of this invention to prepare polyethylene terephthalate exhibiting greatly enhanced color characteristics.

It is another object of this invention to prepare polyethylene terephthalate exhibiting a high degree of luminance combined with a low degree of yellowness.

It is a further object of this invention to prepare polyethylene terephthalate for which the luminance value minus the yellowness value is a maximum.

These and other objects are accomplished in the practice of the present invention which is to prepare polyethylene terephthalate by a direct esterification reaction between terephthatic acid and ethylene glycol or by a transesterification reaction between the methyl ester of terephthalic acid and ethylene glycol to form an ester and the polycondensation of said ester in the presence of a novel catalyst system comprising (1) an antimony compound and (2) an arsenic compound.

The use of the novel catalyst system of this invention results in the production of polyethylene terephthalate of greatly improved color. When using the novel catalyst system comprising l an antimony compound and (2) an arsenic compound, it has been found unexpectedly, that the yellowness value is less than 10 but not substantially less than zero. Of the many catalytic combinations which can be used according to the process of this invention, viz. a catalytic system comprising l an antimony compound and (2) an arsenic compound; all have been found to yield polymers exhibiting high degrees of luminance and a concomitant minimum degree of yellowness. The test results set forth hereinafter amply support these findings.

Furthermore, the novel catalyst system of this invention satisfies all four of the following criteria:

1. High Rate of Reaction.

2. Polymer Color. The polyethylene terephthalate produced using the novel catalyst system of this invention more than satisfies the most stringent color requirements of the textile trade.

3. Polymer Stability. An exceedingly low degradation rate is obtained when the polymers produced using the novel catalyst system of this invention are heated in the molten state.

4. Solubility Characteristics. The novel catalyst system of this invention is substantially soluble in the reaction mixture and in the polymer.

Apart from the enhancement of the color characteristics and rate of polycondensation by the novel catalyst system of this invention, the thermal stability of the resulting polymers is greatly enhanced since compounds comprising the catalyst system remain in the polymer. The presence of the novel catalyst system of this invention greatly enhances subsequent processing operations such as the spinning of fibers and the casting of films which operations are carried out from a polymer melt at elevated temperatures.

The preparation of esters by an ester interchange reaction is generally carried out with a molar ratio of ethylene glycol to dimethyl terephthalate of from about 1:1 to 15:1, respectively, but preferably from about 2:1 to 3:1. The transesterification reaction is generally carried out at atmospheric pressure in an inert atmosphere such as nitrogen, initially at a temperature range of from about C to 290C, but preferably around C to 260C, in the presence or absence of a transesterification catalyst. During the first stage, methyl alcohol is evolved and is continually removed by distillation. Employing procedures heretofore known in the art, the ester interchange portion of the reaction or the first step, requires approximately 1 to 4 hours.

Any known suitable transesterification catalyst may be used in the first stage. The transesterification catalyst is used in concentrations from about 0.01 to 0.2% based on the weight of the dimethyl terephthalate used in the initial reaction mixture. Although the novel catalyst combination of this invention is not, itself, an esterification interchange catalyst, it may, in general be added in the esterification interchange catalyst if desired.

The preparation of esters of terephthalic acid and ethylene glycol by direct esterification reaction is generally carried out with a molar ratio of ethylene glycol to terephthalic acid of from about 1:1 to :1, preferably about 2:1 to 3:1. The direct esterification reaction is carried out at temperatures ranging from about 170C to 290C in the absence of an oxygen containing atmosphere at atmospheric or elevated temperatures for about 2 to 3 hours to form the desired ester product. Air is removed, for example, by purging with nitrogen or other oxygen free inert gas. The polycondensation step, or the polymerization step, of the present invention is effected by adding the novel catalytic mixture comprising an antimony compound and an arsenic compound to an ester, bis-2-hydroxyethyl terephthalate, and heating the mixture thereof under reduced pressure within the range of from about 0.001 millimeters to 100 millimeters of mercury while agitated at a temperature from about 250C to 330C for from 1 to 4 hours. In accordance with this invention, the novel catalyst mixture is generally employed in amounts ranging from about 0.01% to 0.2% based on the weight of the ester to be condensed. Higher or lower concentrations of the novel catalyst mixture of this invention can also be used in the subject polycondensation reaction. 7

In general, antimony compounds which may be used in the practice of this invention include salts of antimony and inorganic acids or organic acids, double salts such as potassium antimony] oxalate and potassium antimony tartrate, and salts of antimony acids such as potassium pyroantimonate. The antimony compounds include antimony salts of aliphatic and aromatic monocarboxylic acids, antimony salts of dicarboxylic acids, e.g. antimony trisglycolate. Typical of the antimony compounds which may be employed as one of the two components of the novel catalyst system of this invention are antimony triacetate, antimony tritallate, antimony tri-2ethylhexoate, antimony oxalate, antimony tributoxide, antimony trichloride, and antimony trioxide.

The antimony compound is of the formula Sb(Y), wherein Y is selected from the group consisting of R, OOCR, O, halogen, OR, SR, OOCRSl-l, SRCOOR',

wherein R and R are independently selected from the group consisting of alkyl, alkenyl, cycloalkyl, aralkyl, aryl, alkaryl, including such radicals when inertly substituted, and n is selected from integers of 3 and 5. The antimony compounds encompassed by this invention include both trivalent and pentavalent antimony compounds.

The antimony compounds include those of the formulae:

I 3-chloropropyl,

wherein n is the valence of antimony, 3 or 5, and a is an integer less than 5 or zero, R and R are as defined above and X is halogen or oxygen.

In this compound, R and R are hydrocarbon radicals preferably selected from the group consisting of alkyl, alkenyl, cycloalkyl, aralkyl, aryl, alkaryl, including such radicals when inertly substituted. Alkyls are typically straight chain alkyl or branched alkyl, including methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, neopentyl, isoamyl, nhexyl, isohexyl, heptyls, octyls, decyls, dodecyls, tetradecyl, octadecyl, etc. Preferred alkyl includes lower al kyl, i.e. having less than about 8 carbon atoms, i.e. octyls and lower. Typical alkenyls include vinyl, allyl, lpropenyl, methallyl, buten-l-yl, buten-2-yl, buten-3-yl, penten-l-yl, hexenyl, heptenyl, octenyl, decenyl, dodecenyl,tetradecenyl, octadecenyl, etc. Typical cycloalkyls include cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, etc. When R is aralkyl, it may typically be benzyl, B-phenylethyl, v-phenylpropyl, B-phenylpropyl, etc. Typical aryls include phenyl, naphthyl, etc. Typical alkaryls include tolyl, xylyl, p-ethylphenyl, pnonylphenyl, etc. R and R may be inertly substituted, e.g. may bear non-reactive substituents such as alkyl, aryl, cycloalkyl, aralkyl, alkaryl, alkenyl, ether, halogen, nitro, ester, etc. Typical substituted alkyls include 2-ethoxyethyl, carboethoxymethyl, etc. Substituted alkenyls include 4-chlorobutyl, v-phenylpropyl, chloroallyl, etc. Substituted cycloalkyls include 4-methylcyclohexyl, 4-chlorocyclohexyl, etc. lnertly substituted aryl includes chlorophenyl, anisyl, biphenyl, etc. lnertly substituted aralkyl includes chlorobenzyl, p-phenylbenzyl, p-methylbenzyl, etc. Inertly substituted alkaryl includes 3-chloro-5- methylphenyl, 2,6-di-tert-butyl-4-chlorophenyl, etc.

Among the antimony compounds used in the practice of this invention are antimony carboxylates.

The anionic component of the antimony carboxylate is expressed in simplest form as R"'(COO'),, wherein R represents a hydrocarbon group, typically an aliphatic or cycloaliphatic group such as alkyl, alkenyl, etc., and corresponding cyclic groups such as cycloalkyl, etc. groups; an aryl group such as phenyl, substituted phenyls, naphthyl, etc.; an aralkyl group such as benzyl, styryl, cinnamyl, etc.; an alkaryl group such as tolyl, xylyl, etc.; a cycloaliphatic group such as a naphthenic group; etc. Other equivalent groups may be employed. Preferably n is l and the acid is monobasic. n may be a small whole integer, typically 1, 2, 3, etc. In the preferred embodiment, R may be an alkyl group having less than about 20 carbon atoms. Typical of the acids from which the antimony salts may be prepared may be acetic acid, propionic acid, butyric acid, caproic acid, caprylic acid, capric acid, stearic acid, oleic acid, etc. Naphthenic acid may be employed. The commercially occurring mixture of acids known as tall oil fatty acids are preferred in the practice of this invention.

lt is preferred that the antimony carboxylate be formed from an amount of acid sufficient to satisfy each of the valence bonds of the antimony metal. The salts which may be used in practice of this invention may be those materials prepared for example by neutralizing a basic compound of the metal, typically the hydroxide or oxide.

Specific antimony compounds operable in the practice of this invention include:

antimony tritallate antimony-Z-ethylhexoate antimony tristearate antimony trilaurate antimony trimyristate antimony tripalmitate antimony trioleate antimony triricinoleate antimony trinaphthenate antimony tribenzoate antimony trisalicylate antimony triphenoxide antimony tricresoxide antimony trixylenoxide antimony nonylphenoxide antimony caproate diheptylate antimony tricaprylate dibromide antimony tributyrate dibromide antimony tricinnamate dibromide antimony trivalerate dibromide antimony triheptylate dibromide antimony tricaprate dibromide tris(2,3-dichloropropyl) antimonite tris( ,B-chloroethyl) antimonite tris( B-chlorobutyl) antimonite tris(2-chloro-2-phenylethyl) antimonite tris(n-octoxy) antimony dibromide tris(2-ethylhexoxy) antimony dibromide tribenzoxy antimony dibromide tris(B-chloroeth0xy) antimony dibromide tris(B-chlorobutoxy) antimony dibromide phenyl antimony dibromide tolyantimony dibromide butylantimony diiodide benzylantimony dichloride cyclohexylantimony dibromide allylantimony diiodide chlorophenylantimony dichloride octylantimony dibromide diphenylantimony acetate diphenylantimony propionate diphenylantimony butyrate ditolylantimony a-methylpropionate dixylylantimony a-methylpropionate di-a-naphthylantimony acetate ditolylantimony butyrate bis(p-chlorophenyl) antimony v-chlorobutyrate diphenylantimony B-ethoxypropionate diethylantimony acetate di-n-propylantimony propionate di-n-butylantimony a-methylpropionate di-n-octylantimony propionate dilaurylantimony butyrate bis(2-ethylhexyl) antimony a-methylpropionate di-n-hexylantimony acetate diallylantimony acetate di-Z-butenylantimony propionate dibenzylantimony a-methylpropionate dicyclohexylantimony acetate diphenylantimony valerate diphenylantimony caproate ditolylantimony a-methylvalerate dixylylantimony B-methylvalerate diethylantimony a-ethylcaproate di-n-propylantimony caprylate dim-butylantimony caprate di-a-naphtylantimony pelargonate di-n-octylantimony laurate dilaurylantimony stearate di-2-ethylhexylantimony oleate di-n-hexylantimony benzoate diallylantimony p-toluate di-2butenylantimony p-ethylbenzoate dibenzylantimony a-naphthoate dicyclohexylantimony phenylacetate diphenylantimony phenoxya'cetate diphenylantimony linoleate ditolylantimony cyclohexanoate diphenylantimony tetrachlorbenzoate diphenylantimony tallate ditolylantimony rosinate bis(p-chlorophenyl) antimony pelargonate diphenylantimony p-chlorobenzoate diphenylantimony dithiocarbamate dibutylantimony methyldithiocarbamate diphenylantimony dimethyldithiocarbamate ditolylantimony ethyldithiocarbamate diallylantimony diethyldithiocarbamate phenylantimony di-( n-propyldithiocarbamate) tolylantimony di(di-n-propyldithiocarbamate) butylantimony di(isopropyldithiocarbamate) allylantimony di( diisopropyldithiocarbamate) I benzylantimony di(butyldithiocarbamate) cyclohexylantimony di(dibutyldithiocarbamate) chlorophenylantimony di(octyldithiocarbamate) octylantimony di(dioctyldithiocarbamate) dibenzylantimony dodecyldithiocarbamate dichlorophenylantimony didodecyldithiocarbamate dicyclohexylantimony hexadecyldithiocarbamate dioctylantimony phenyldithiocarbamate diphenylantimony diphenyldithiocarbamate dicyclohexylantimony cyclohexyldithiocarbamate phenylantimony di(dicyclohexyldithiocarbamate) tolylantimony di( allyldithiocarbamate) cyclohexylantimony di(diallyldithiocarbamate) diphenylantimony benzyldithiocarbamate dibenzylantimony dibenzyldithiocarbamate di(diphenylantimony) methylenebisdithiocarbamate di( ditolylantimony) ethylenebisdithiocarbamate di(dicyclohexylantimony) propylenebisdithiocarbamate phenylantimony trimethylenebisdithiocarbamate tolylantimony tetramethylenebisdithiocarbamate butylantimony hexamethylenebisdithiocarbamate allylantimony octamethylenebisdithiocarbamate benzylantimony o-phenylenebisdithiocarbamate phenylantimony m-phenylenebisdithiocarbamate di(diphenylantimony) p-phenylenebisdithiocarbamate di(ditolylantimony) a-tolylenebisdithiocarbamate chlorophenylantimony xylylenebisdithiocarbamate di(diphenylantimony) 4,4'-biphenylene bisdithiocarbamate di(diphenylantimony) 4-chlorol ,2-phenylenebisdidichlorophenylantimony cyclo hexyldithiocarbamate N-( 3-chloro-2-butenyl octylantimony di(N-cyclohexyl amyldithiocarbamate) antimony S,S,S" tri(octadecyl thiomaleate) mercaptoacantimony S,S,S" tri(dihydroabietyl etate) antimony S,S',S" tri(nonylmercaptoacetate) tate) Other antimony compounds operable as components trimethylstibine triethylstibine tributylstibine trioctylstibine trivinylstibine triphenylstibine pentaphenylstibine methyldichlorostibine butyldichlorostibine octyldichlorostibine lauryldichlorostibine vinyldichlorostibine phenyldichlorostibine methyldichlorostibine dichloride octyldichlorostibine dichloride phenyldichlorostibine dichloride dimethylchlorostibine dibutylchlorostibine dioctylchlorostibine diphenylchlorostibine dimethylchlorostibine dichloride dibutylchlorostibine dichloride trimethylstibine dichloride tributylstibine dichloride trioctylstibine dichloride triphenylstibine dichloride triphenylstibine iodide cyanide tetraethylstibonium iodide stibosobutane stibosooctane stibosobenzene thiostibosobenzene triethylstibine oxide tributylstibine oxide trioctylstibine oxide triphenylstibine oxide .tributylstibine sulfide methylstibonic acid octylstibonic acid phenylstibonic acid dimethylstibinic acid dibutylstibinic acid dioctylstibinic acid dioctadecylstibinic acid diphenylstibinic acid butyldioctoxystibine phenyldibutoxystibine butyldithiolaurylstibine butyldiacetoxystibine octyldiacetoxystibine phenyldiacetoxystibine butylantimony dilaurate octylantimony dibenzenesulfonamide dibutylbutoxystibine of the novel catalyst system of this invention include:

dibutylaceloxystibine diphenylacetoxystibine dibutylthiolaurylstibine dibutylantimony benzenesulfonamide bis(dimethylantimony) oxide bis(dibutylantimony) oxide bis(dioctylantimony) oxide bis(diphenylantimony) oxide bis(dibutylantimony) sulfide bis(diphenylantimony) sulfide tetramethyldistibine tetraethyldistibine tetraoctyldistibine tetraphenyldistibine Extensive testing of a large variety of arsenic sacrificial catalysts has indicated that, while they vary somewhat in their activity, all arsenic compounds possess outstanding catalystic activity of a sacrificial nature, as demonstrated in test results later described. The arsenic compound may have one or more bonds from arsenic to one or more organic radicals to halogen, hydrogen, oxygen, sulfur or nitrogen atoms. Among the many types of such compounds containing arsenic of which specific representative compounds have teen tested and shown to be active are: arsenic trioxide, arsenic tristearate, arsenic tritallate, arsenic triacetate, tributylarsine, trioctylarsine, tribenzylarsine, trivinylarsine, and triphenylarsine. Other compounds having at least one carbon to arsenic bond which the remaining valences of the triand pentavalent atoms are taken up by bonds to hydrogen, halogen or hydroxyl atoms include octylarsine, octylidichloroarsine, phenyldimercaptoarsine, dichloroarsine, phenyldimercaptoarsine, phenylarsenic sesquisulfide, octyldichloroarsine dichloride, phenyldichloroarsine dichloride, dibutylarsine, dioctylchloroarsine, diphenylchloroarsine, dibutylchloroarsine dichloride, and tetrabutylarsonium hydroxide. Other arsenic compounds having at least one double bond from arsenic to oxygen or sulfur are also efficacious. These include arsenosooctane, arsenosobenzene, thioarsenosododecane, isoamylarsenic disulfide, tributylarsine oxide, triphenylarsine oxide, and tributylarsenic sulfide. Other arsenic compounds having at least one double bond from arsenic to oxygen or sulfur and in addition at least one bond from arsenic to a halogen atom or a hydroxyl group are also useful. These include phenyldichloroarsine oxide, octylarsonic acid, phenylarsonic acid, and diphenylarsinic acid. Other arsenic compounds having at least one direct bond from carbon to arsenic and the remaining valences occupied by bonds to oxygen, sulfur or nitrogen linking organic radicals to the arsenic atom are also useful. These include butyldioctoxyarsine, lauryldiphenoxyarsine, phenylarsenic dilaurate, octylarsenic dibenzenesulfonamide, methyldithiolaurylarsine, dibutylbutoxyarsine, dibutylphenoxyarsine, dibutylacetoxyarsine, dibutylarsenic laurate, dibutylarsenic toluenesulfonamide, and dibutylthiolarsine. Other arsenic compounds having two or more arsenic atoms that may or may not be bonded to one another but at least have one carbon atom bonded to each arsenic atom and possibly also bonds from the arsenic atom to hydrogen, halogen, oxygen, sulfur or nitrogen are also operable. Such compounds include arsenopropane, arsenobenzene, bis(dibutylarsenic) oxide, bis(dioctylarsenic) oxide, bis(diphenylarsenic) oxide, and bis(dibutylarsenic) sulfide.

It is to be understood that the organic radicals linked to the arsenic atoms directly or through oxygen, sulfur or nitrogen need not be the same in any given compound and that the structure of the compound need not in any sense be symmetrical.

The novel catalyst system of this invention can be added in any suitable amount, preferably in an amount between 0.005 and 1% by weight based on the weight of bis(B-hydroxyethyl) terephthalate used. The ratio of arsenic compound to antimony compound in the catalyst system should be between 0.01 and 1, preferably about 0.1 or lower. An ester interchange catalyst may be used in the first stage. Many such catalysts are known. They include alkaline earth salts and such compounds as titanium dioxide, calcium acetate, and zinc acetate. The novel polycondensation catalyst system of this invention may in certain instances, be added to an ester interchange reaction mixture if desired, but it has been found that is is preferable, in some instances, to add the polycondensation catalyst after deactivation of the ester interchange catalyst. This later addition results in the obtaining of polymers having high degrees of luminance and low degrees of yellowness.

The following examples illustrate this invention particularly with respect to the preparation of highly polymeric polyethylene terephthalate by starting with bis(B-hydroxyethyl) terephthalate. The catalyst of this invention is also operable in catalyzing the polymerization of other esters of terephthalic acid such as the ethyl, propyl, butyl, and phenyl esters. The polymerization of esters of other organic acid compounds are also catalyzed by the novel catalyst system of this invention. These include esters of adipic acid, butyric acid, sebacic acid, maleic acid, tetrachlorophthalic acid, phthalic acid, cyclohexane, carboxylic acid, cyclohexane dicarboxylic acid, benzoic acid, paramethyl benzoic acid, etc. Anhydrides and half esters of these acids may be employed. In practice of the invention, the term acid compound may herein be used to include these anhydrides and half esters as well as the acids. Typical of the anhydrides may be phthalic anhydrides, acetic anhydride, maleic anhydride, etc.; typical of the half esters may be, e.g. isooctyl acid phthalate, isooctyl acid maleate, etc.

EXAMPLE 1 This examples illustrates a complete two-step process in the preparation of polyethylene terephthalate from dimethyl terephthalate and ethylene glycol.

2000 parts by weight of dimethyl terephthalate, 1400 parts by weight of ethylene glycol, and 0.3 parts by weight of zinc acetate were heated in a three-necked flask, equipped with a stirrer and a condenser at atmoshperic pressure until that quantity of methanol theoretically calculated to evolve had been distilled off (viz. 836 milliliters of methanol). The zinc acetate esterification catalyst was sequestered by adding 1.38 parts of tri-nonylphenyl phosphite, stirring and heating the reaction mixture for minutes. The bis(B- hydroxyethyl) terephthalate product was then isolated.

1000 grams of the bis (,B-hydroxyethyl) terephthalate monomer and 0.5 grams of antimony triacetate, 0.03 grams of arsenic triacetate and 3.8 grams of titanium dioxide were added to a polyester reactor preheated to 260C. The temperature of the reactor was then adjusted to 280C simultaneously with the application of a vacuum of 0.5 millimeters of mercury. The polymerization was allowed to proceed for 150 minutes. The ethylene glycol formed as a'result of the polymerization was distilled off and collected. Upon cooling, the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.75 and a melting point of 262C.

The reflectance of a plaque of the polymer product was measured on a Colormaster. The luminance was 68 and the yellowness was 10, the L-Y value being 58.

EXAMPLE 2 The process of Example 1 was followed except that the charge to the polymerization reactor consisted of 1000 grams of bis(B-hydroxyethyl) terephthalate and 0.0125 grams of antimony triacetate, and 0.025 grams of arsenic pentoxide. The polymerization reaction was allowed to proceed for 3.75 hours. Upon cooling, the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.80 and a melting point of 265C.

The reflectance of a plaque of the polymer product was measured on a Mecco Colormaster. The luminance was 62 and the yellow index was 7; the L-Y value being 55.

The novel catalyst system of this invention, viz. a system comprising a mixture of (1) an antimony compound and (2) an arsenic compound, results in a polymer exhibiting an outstanding color as shown in comparative examples hereinafter:

A polyethylene terephthalate polymer made under the same conditions and using the same equipment as that of Example 2 except that 0.5 grams of antimony triacetate alone was used as the polycondensation catalyst exhibited a luminance of 65 and a yellowness of 21, i.e. a L-Y value of 44.

The yellowness of a polymer made using the catalyst system of this invention was 14 units better than that using an antimony catalyst alone.

EXAMPLE 3 The process of Example 1 was followed except that the charge added to the polymerization reactor consisted of 1000 grams of bis(B-hydr0xyethyl) terephthalate, 0.5 grams of antimony triacetate (0.05% of the weight of the monomer), 0.05 grams of triphenylarsenic oxide, and 3.8 grams of titanium dioxide. The polymerization reaction was allowed to proceed for 3.5 hours. Upon cooling the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.76 and a melting point of 261C.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance was 65 and the yellowness was 8, the L-Y value being 57.

EXAMPLE 4 The process of Example 1 was followed except that the charge to the polymerization reactor consisted of [000 grams of bis(B-hydroxyethyl) terephthalate, 03.43 grams (0.343% of the weight of the monomer) of antimony tristallate, 0.10 grams of arsenic tritallate, and 3.8 grams of titanium dioxide. The polymerization reaction was allowed to proceed for 3.5 hours. Upon cooling, the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.77 and a melting point of 246C.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance was 48 and the yellowness was 0, the L-Y value being 48.

EXAMPLE The process of Example 1 was followed except that the charge added to the polymerization reactor consisted of 1000 grams of bis( B-hydroxyethyl) terephthalate, 0.5 grams (0.5% of the weight of the monomer) of antimony triacetate, 0.05 grams of phenylarsonic acid, and 3.8 grams (0.38% of the weight of the monomer) of titanium dioxide. The polymerization reaction was allowed to proceed for 2 hours. Upon cooling the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.79 and a melting point of 262C.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance was 64 and the yellowness 12, the L-Y value being 52.

EXAMPLE 6 The process of Example 1 was followed except that the charge added to the polymerization reactor consisted of 1000.0 grams of bis(B-hydroxyethyl) terephthalate, 1.0 grams (0.10% of the weight of the monomer) of antimony triacetate, 0.10 grams (0.10% of the weight of the monomer) of triphenylarsine, and 3.8 grams (0.38% of the weight of the monomer) of titanium dioxide. The polymerization reaction was allowed to proceed for 3.5 hours. Upon cooling, the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.84.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance value was 52 and the yellowness 3,- resulting in an L-Y value of 49.

EXAMPLE 7 The process of Example 1 was followed except that the charge added to the polymerization reactor consisted of 1000.0 grams of bis(B-hydroxyethyl) terephthalate and 0.5 grams of (0.05% of the weight of monomer) of antimony triacetate, 0.0032 grams of arsenic pentoxide- (0.0032% of the weight of the monomer), and 3.8 grams of titanium dioxide. The polymerization reaction was allowed to proceed for 4 hours. Upon cooling, the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.74.

For the purposes of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corpo- EXAMPLE 8 The process of Example 1 was followed except that the charge to the polymerization reactor consisted of 1000 grams of bis(B-hydroxyethyl) terephthalate and 3.43 grams (0.343% of the weight of the monomer) of anatimony tristallate, 0.10 grams (0.01% of the weight of the monomer) of arsenic tristallate, and 3.8 grams (0.38% of the weight of the monomer) of titanium dioxide. The polymerization reaction was allowed to proceed for 3.5 hours. Upon cooling the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.77 and a melting point of 261C.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance value was 48 and the yellowness 0, resulting in an L-Y value of 48.

EXAMPLE 9 The process of Example 1 was followed except that the charge added to the polymerization reactor consisted of 1000 grams of bis(B-hydroxyethyl) terephthalate and 3.43 grams (0.343% of the weight of the monomer) of antimony tristallate, 0.10 grams (0.01% of the weight of the monomer) of arsenic tristearate and 3.8 grams (0.38%of the weight of the monomer) of titanium dioxide. The polymerization reaction was allowed to proceed for 3.5 hours. Upon cooling the polyethylene terephthalate product exhibited an intrinsic viscosity of 0.79 and a melting point of 260c.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance value was 56, the yellowness 5,

and the L-Y value 51.

EXAMPLE 10 The process of Example 1 was followed except that the charge to the polymerization reactor consisted of 1000 grams of bis(B-hydroxyethyl) terephthalate and 1.0 grams of antimony triacetate (0.10% of the weight of the monomer), 0.10 grams of triphenylarsine (0.01% of the weight of the monomer), and 3.8 grams of titanium dioxide (0.38% of the weight of the monomer).

The polymerization reaction was allowed to proceed EXAMPLE 11 The process of Example 1 was followed except that the charge'added to the polymerization reactor consisted of 1 000 grams of bis(B-hydroxyethyl) terephthalate, and 0.5 grams (0.05% of the weight of the monomer) of antimony triacetate, 0.0063 grams (0.00063% of the weight of the monomer) of arsenic trioxide, and 3.8 grams (0.38% of the weight of the monomer) of titanium dioxide. The polymerization reaction was allowed to proceed for 3.5 hours. Upon cooling the poly ethylene terephthalate product exhibited an intrinsic viscosity of 0.81 and a melting point of 261C.

For the purpose of comparing the yellowness and luminance of samples of polyethylene terephthalate product, the reflectance of the polymer was measured on a Colormaster which is the trade name for the differential colorimeter manufactured by the Mecco Corporation. The luminance value was 65, the yellowness l0, and the L-Y value 55.

To illustrate the dramatic enhancement of the color properties effected by the use of the catalyst system of this invention comparison polymerizations were conducted using the same equipment and the same conditions as used in Examples 1 through 1 1. These comparison or control polymerizations differed only in that 0.5 grams of germanium dioxide (0.05% of the weight of the monomer) wass used in one polymerization. After 3.5 hours of reaction the resulting polymer exhibited a luminance value of 71, a yellowness index of 22, and a L-Y value of 49.

To show that antimony compounds alone used as a catalyst will not effect the dramatic color enhancement, a further polymerization was conducted using antimony triacetate as a polymerization catalyst. The polymerization was conducted under conditions and amounts identical with those of the foregoing examples:

Without the presence of an arsenic compound, polyethylene terephthalate polymerized in the presence of antimony triacetate exhibited a luminance of 65 and a yellow index of 21, and a L-Y value of 44.

Table I sets forth the luminance values, the yellowness values, and the L-Y values for each of the foregoing Examples and for the comparison polymers polycondensed in the presence of catalysts other than the novel catalyst system of this invention.

The foregoing data show the dramatic and unexpected decrease in yellowness obtained by the use of the novel catalyst system of this invention.

The products of this invention exhibit enhanced flame resistance. As an added feature of this invention the novel catalysts of this invention act as internal lubricants such that the spinning of the products into fibers is greatly facilitated.

Although this invention has been illustrated by reference to specific examples, numerous changes and modifications thereof which clearly fall within the scope of the invention will be apparent to those skilled in the art.

We claim:

1. A process for preparing polyethylene terephthalate of improved color, as determined by the difference between the luminance value and yellowness index of the polymer, wherein dimethyl terephthalate is reacted with ethylene glycol to form an ester of ethylene glycol and terephthalic acid or where terephthalic acid is reacted with ethylene glycol to form an ester of terephthalic acid and ethylene glycol wherein the resulting ester is polycondensed in the presence of a catalytic amount of a polycondensation catalyst consisting of a. an antimony compound having one of the following formulae:

Sb(Y),, or Y Sb O; and

b. an arsenic compound having one of the following formulae:

As(Y),,, AS203, As O or Y As=O,

wherein n is 3 or 5 and each Y is individually selected from the group of monovalent radicals consisting of R, OOCR, OR, SR, OOCRSH and SRCOOR wherein R is in turn selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl and alkaryl radicals and R is a divalent radical selected from the group consisting of alkylene, c'ycloalkylene, arylene, aralkylene and alkarylene radicals.

2. A process as described in claim 1 wherein the antimony compound exhibits the formula Sb(OR),, or Sb(OOCR),,.

3. A processs as described in claim 2 wherein the antimony compound is antimony triacetate or antimony tritallate.

4. A process as described in claim 2 wherein the anti- 'mony compound is antimony tributoxide.

5. A process as described in claim 1 wherein the arsenic compound is arsenic trioxide or arsenic pentoxide.

6. A process as described in claim 1 wherein the arsenic compound exhibits the formula As( OOCR),,'or As- 7. A process as described in claim 6 wherein the arsenic compound is arsenic triacetate, arsenic tritallate or arsenic tristearate. 

1. A PROCESS FOR PREPARING POLYETHYLENE TEREPHTHALATE OF IMPROVED COLOR, AS DETERMINED BY THE DIFFERENCE BETWEEN THE LUMINANCE VALUE AND YELLOWNESS INDEX OF THE POLYMER, WHEREIN DIMETHYL TEREPHTHALATE IS REACTED WITH ETHYLENE GLYCOL TO FORM AN ESTER OF ETHYLENE GLYCOL AND TEREPHTHALIC ACID OR WHERE TEREPHATHALIC ACID IS REACTED WITH ETHYLENE GLYCOL TO FORM AN ESTER OF TEREPHATHALIC ACID AND ETHYLENE GLYCOL WHEREIN THE RESULTING ESTER IS POLYCONDENSED IN THE PRESENCE OF A CATALYTIC AMOUNT OF A POLYCONDENSATION CATALYST CONSISTING OF A. AN ANTIMONY COMPOUND HAVING ONE OF THE FOLLOWING FORMULAE:
 2. A process as described in claim 1 wherein the antimony compound exhibits the formula Sb(OR)n or Sb(OOCR)n.
 3. A processs as described in claim 2 wherein the antimony compound is antimony triacetate or antimony tritallate.
 4. A process as described in claim 2 wherein the antimony compound is antimony tributoxide.
 5. A process as described in claim 1 wherein the arsenic compound is arsenic trioxide or arsenic pentoxide.
 6. A process as described in claim 1 wherein the arsenic compound exhibits the formula As(OOCR)n or As(OR)n.
 7. A process as described in claim 6 wherein the arsenic compound is arsenic triacetate, arsenic tritallate or arsenic tristearate. 